1. Technical Field
The present invention relates to a travel control apparatus for a vehicle that employs an automatic driving technique.
2. Related Art
Recently, various apparatuses employing automatic driving techniques have been developed and proposed for use in vehicles with the aim of allowing a driver to drive the vehicle in increased comfort and more safely. For example, Japanese Unexamined Patent Application Publication No. 2011-189803 (JP-A) discloses a technique employed in a vehicle control apparatus that restricts a control amount of a part of a plurality of actuators such as an engine, an automatic transmission, an electric power steering apparatus, a variable steering gear ratio system, and a brake oil pressure control apparatus in accordance with a reliability of information detected by a camera, a radar, a navigation system, and so on. More specifically, a lateral direction of a vehicle equipped with the vehicle control apparatus is recognized by the camera, a travelable region in the lateral direction is set in accordance with the reliability of the camera, an obstruction in a front-rear direction of the vehicle is detected by the radar, a travelable region in the front-rear direction of the vehicle is set in accordance with the reliability of the radar, and in response to information from the navigation system, travelable regions in the front-rear and left-right directions are set in accordance with the reliability of the navigation system (a condition of a global positioning system (GPS) satellite). The travelable regions in the front-rear direction and the left-right direction of the vehicle are then compared with the travelable regions set in accordance with the reliability of the navigation system, and the travelable regions having smaller values are confirmed as the travelable regions in the respective directions. By confirming the travelable regions in this manner, travel control executed in the lateral direction by the electric power steering apparatus and the variable steering gear ratio system can be restricted in a case where the reliability of the information detected by the camera is low, and a control amount applied by the brake oil pressure control apparatus can be restricted in a case where the reliability of the information detected by the radar is low.
Incidentally, in the case of the vehicle control apparatus disclosed in JP-A, as described above, the front-rear direction travelable region set in accordance with the reliability of the radar and the left-right direction travelable region set in accordance with the reliability of the camera are compared with the travelable regions set in accordance with the reliability of the navigation system, and the travelable regions having the smaller values are confirmed as the travelable regions in the respective directions. When the reliability of the camera (and image information obtained from the camera) is low, for example, such that the left-right direction travelable region set in accordance with the reliability of the camera decreases in size, the final left-right direction travelable region is also set to be small, with the result that vehicle control is not performed in the lateral direction even though map information provided by the navigation system exhibits high reliability. In practical terms, therefore, automatic driving control becomes difficult. Hence, automatic driving of the vehicle may be continued using the map information, but depending on the provided map information, it may be impossible to implement precise, stable automatic driving continuously without appropriately varying the form of the automatic driving. Moreover, it must be possible to shift the control appropriately in response to steering input from the driver without contradicting the steering intentions of the driver.